With reduced wind flow velocity - the higher you can 'point' ... several factors combine to make this happen.
1. the relative
speed of the boat vs. the relative
speed of the oncoming air ... creates a slightly larger 'relative
' amplitude 'upwash' of air flow in front of the boat - for higher angle of attack relative
to the 'true' wind.
2. the 'slot distance' between the jib and main is (should be) more closed or reduced in light winds vs. higher strength winds ... giving a boat in light winds a higher 'angle of attack' relative to the 'true' wind because the clew can (should) be closer to the boats centerline than when in 'heavier' wind as well as better 'aerodynamic dumping velocity' (bootstrapping) between the jib and main. You precisely adjust the 'slot distance' in accordance to the output of the speedo (and forget or ignore any so-called 'backwinding' you see in the luff of the main) .... max speed is the goal when adjusting how far open or closed that 'slot' is. Of course your sails are perfectly trimmed and shaped (all tell tales flying 'perfect') and with VERY slight 'weather helm', before
you adjust the slot-open distance to get MAX. SPEED/VMG out of the boat when beating!!!
For the case of the shoaldrafter and pointing ability, you have several things against you:
1. a shoaldrafted boat will more easily skid to leeward (helmsman erroneously blaming 'weather helm' because of the side-impact of water against the rudder due to the normal skid) .... so, the position of maximum draft of both sails has to be 'more forward' AND the wake coming off the stern is at an angle of no more than 2-3°. The usual 'set up' is to get MAX. speed out of a shoaldrafted boat when attempting to 'beat' (to maximize VMG) by having a near 'dead fish' / neutral helm with *VERY* slight helm pressure and by checking the stern wake (turbulence caused by the keel and rudder ... is coming STRAIGHT off the stern, not any appreciable angle .... get that boat MOVING instead of skidding to the lee (for better VMG!!). With a near dead-fish helm you will consciously have to work the wheel/tiller for the boat to go 'upwind' and not constantly 'bear off'.
Also you will have to learn how to 'turbo sail' : Footing Off - SailboatOwners.com
.... post#12 and this also applies to deep fin keelers who want to 'fly' their keels.
2. You're simply not going to get that shoal draft keel to develop very much LIFT to weather, in comparision to a deep fin.