Yes the large meplat and for the 10MM, probably higher velocity is what chopped the larger exit hole. The same happens in game. Both 'wound channel' and straight penetration. I sure don't know everything there is to know about straight penetration, but I know and understood very well that meplat size is critical. If either too small or too large a non deforming bullet will tumble or yaw off coarse, in both case hurting the kill power of the bullet. Full wadcutters will not penetrate true for very long distences, yet just a little upset of the nose of a full wadcutter will make it penetrate true.
We all shoot at wood to test bullet performance but it is a very poor test medium, other than for penetraton. If you want to get a good relitive picture of killing power, line up a row of plastic containers filled with water. Milk jugs are ideal. A full load behind the 28 180 FN LBT bullet will punch a straight line through at least 6 one gallon milk jugs. The most impressive thing is that every one of them will burst with severe force. Hit the same row of jugs with a 125 gr JHP and only the first till rupture, very forcefully of coarse, but normally the bullet will not even reach the second jug. The bullets you tested would probably go the length of 6 jugs, with the other bullets you used, if they stayed on coarse, but the difference in 'kill' anmistered to each would be startling, even more than the hole in your spruce log.