Most of us have the opposite problem on SIB's and you need to add a wooden spacer block to raise the engine 1" or so. Certainly on the Aerotec and Zodiacs this is essential.
Best way to measure the set up is to get a cheap tiny tach off eBay (about £10) and measure the RPM at WOT with this and the speed with a GPS to fine tune trim and engine height.
Having said that 9/10 postion 2 is always the one and a block is needed as above.
Did mine last week and position (1) got me 5450 rpm and 17.5 kts or so, position (3) 5650 rpm and 18 kts (but horrible to get on plane due to raised bow) but position 2 wins at 5750 rpm and maxed out briefly at 19 kts.