Gentleman,, the missing piece of your puzzle is PORTFOLIO MARGIN,
i do not have standard reg t , if you do not know about pm,, heres a link for some explanation, https://en.wikipedia.org/wiki/Portfolio_margin ,, , further more, my 25 years at this game has led me to my approach which is specific, very far away strikes with very short DTE, i bascially provide a service to everyone who does credit spreads, i furnish good prices on the outer legs,, i started in 1994 with 38k doin OEX spreads ,,then it got real serious in 98 as a SOES bandit to 2002 and in 2006 the gates of heaven opened up, i got portfolio margin, GAME CHANGER.. in addition to my approach came weeklys around 2010,, i have taken 4 major hits since 1994 -- 1998,2010-2015 and 2018 18-30% of my portfolio , it just takes a few months to make it back and i still managed to Beat the S&P since 1998,,, as for the non option position of TVIX ,, since that COntango stock floated in 2009 i have shorted 100- 3000 shares a day every, it a depreciating asset just look at the 10 yr chart, it just keeps reverse splitting, again, major mkt drops this can get a lil hairy,, we keep at it,, look im not selling any thing, im not pitching anything,, and NO I did NOT LOSE MY MIND, and im NOT a ticking time bomb , im focused , i have refined my approach to fit my stocks and my comfort level, and that took time ,many years ,,im always learning like everyone else here , the differences with IB and TD is concentration risk,, yes 10 contracts may be less margin at IB,,but when you start to do size 1000 contracts TD risk profile are more favorable , the FUND im referring to is called FOSTER GLENWOOD and we have 3 accounts that make up the account , TD ,IB and ICBC,,,, we know what positions works best at each firm,,,you have to have a strong work ethic, and a really positive attitude and the smarts to be creative to find all the hidden high probability . positions, also,, working for a small firm margin .risk and trade desk, along with helping people im blessed to get to see thousands of clients accounts and how they make or lose money,, the ones who make money only trade 1 to 5 names, the rest who trade many names ,mostly lose money,, as for the and i dont think i ever ask for vaseline , im just addressing all the unknown chatter here,, when asked i DO explain in detail of any position i have, ,,i DONT bull shit, i dont play games I DONT advise ,,i TRADE and i help others ,if you wish to know more feel free to ask, i can be found on the options traders forum on Facebook,
Wow, we’ve got living legend on ET

Rick, thanks, I’ve seen several of your responses about portfolio margin and appreciate those, but I just can’t reconcile them with my own portfolio margin accounts, therefore trying to gather whatever info I can from other people.
I’ve looked at a few live and demo PM accounts at IB and TDA, and they not only seem to provide different base margin/bp (between IB and TDA) but also the bp/margin use varies based on our positions, differently at different brokers. Some brokers like TastyTrade totally screw up margin calculations, for example when legging-into spreads (Tasty wouldn’t recognize those as spreads) and admitted to bugs in margin calculation they’re yet to fix. TDA and IB are better at margin calculation and assessing total portfolio risk, but differ between each other, and possibly even between customers. You may see $x available margin and simply use it as you please, but there may be underlying margin calculation based on your existing positions, and possibly other factors (account size?).
Overall IB seems to give me better margin than TDA but still not enough to sell too many naked options. On another hand, someone on FB showed me their TDA account where selling some naked equity options used less buying power than at IB.
Those differences will continue bugging me because I can’t trade professionally without understanding all factors that contribute to and account for those differences. I’m even thinking about closing all my positions at IB and moving to TDA just to check whether a larger PM account size would matter, but that would be a lot of trouble. Thus for now I’m trying to find out if anyone with TDA account could explain why/when/how you guys may end up with better margin than at IB.
Though I’m also aware that you’re doing some financial engineering and sometimes buy a few 5-cent options to offset the sold ones.
My margin use varies wildly at IB from day to day, even without practical risk, and I’m just looking for ways to master it.