I have this problem, that Slam Tilt (AGA) does not start when loaded from
OS 3.9, but loads fine when started without startup-sequence, and with preload option used. The game requires 2 mb chipmem and 1mb othermem.
I assume that when loaded from OS, the chipmem runs out (just black screen, have to boot from that point). Is there a tooltype that forces whdload to use only or mostly Fast ram? Or is this even my problem ?
Thanks again. 
Try booting 3.9, then select a low-res screenmode with 4 colors to free some chipmem. If the game then works, you've narrowed it down.
If it's a chipmem issue, see
this thread for some ideas. I play SlamTilt from WB all the time, so it's definitely "doable".

(My apologies if you've already tried all this.) There aren't any WHDLoad tooltypes I'm aware of to help here.