What actually is scale-in/-out anyway?!
I would think that usually an always-in-the-market SAR system (based on EOD data) would require to Exit all existing position(s) while the old trend finishes in order to Enter new position(s) while a new trend starts to develop.
1. According to Perry Kaufman (Trading Systems and Methods, page 617), the building up (or adding) of positions to a trade (at pre-set intervals for the effect of a single poor entry point is reduced and a better average entry price is created) is called Scaled-down buying (for normal profits) while a trend starting.
2. According to Larry William (Long-term Secrets to Short-term Trading, page 183), we need to first determine the (constantly updated) Number of contracts to trade: which is equal to (Account balance which is gradually increased when a trend is favourbly developed)* (Risk percent pre-defined, say average 5%) / (Largest loss willing to take when executing the system). This could be called Scaled-up buying (for additional profits) while riding a trend.
3. However, separately to the above, extra trades for pullback/ retracement can be optionally established, these individually buying/selling position(s) due to pullback/ retracement while riding a trend could be called Load-the-boat buying (for extra profits), through taking extra risk (say, maximum another 5%).
4. Personally I would believe that whether to scale in (within the same bar or across multiple bars) or not (using single order or multiple smaller orders) for building up the position(s) equating to the said 5% risk twice (or more) separately and independently in all three situations for normal/ additional/ extra profits would be simply a personal preference, imo, as long as the market allows (which would be completely another issue!).
