In SD, no spread at all is needed when both rules and penetration are excellent. A good CC can theoretically get +EV via Ins. and Play decisions only.
The above sure felt good when I typed it in. What I usually do in SD is as follows:
(1) PLAYING ONE HAND ONLY...bet 2 Units "off the top", then dropping to 1U when the Count goes neg., and increasing to 4U when "appropriately" pos. For cover, often, BUT NOT ALWAYS, make a 3U bet in MARGINALLY pos. counts. And likewise, often after a win, will leave a 2U bet ride in a MARGINALLY neg. count.
------Advantage...generally accepted, generally "ploppyish", no 12+:1 swings to garnish attention, appears to be both semi-progressive and semi-martingale, based on prior hand results. Creates an ave. 4:1 spread...OK, I mean an ave. 3.72586777 spread, but you get my drift.
------DisAdvantage...once you are good at CC'ing, SD is EASY! Gets kind of boring, esp. in Neg. swings of the B/R. Also, in SD, a -6 TC after the first deal, may often be +7 after the second round...do not get greedy and "over-ramp"!
(2) PLAYING TWO HANDS...off the top bet two hands of 2U each. Raise to 2x4 at appropriately + Counts, and dropping to 1x1 in Neg. Counts. As above, Advantages and DisAdvantages similar...works best when "Mid-Shoe" entry is allowed...when not, carefully "over-ramp/under-ramp" bets as allowed, as determined by the ambient air temperature.
This "System" creates an ave. 8:1, I mean 7.74363299 Spread.
I hope this has been helpful. Certainly, there are much better systems for the WONGER's (IMHO, WATCHER's), but if YOU WANT TO PLAY BJ, this works pretty well, as long as you move alot.
ph7.