Hey,
I have never tried heating the head more, thanks dr del that makes good sense! Adam Wysocki 8 ball python comment of pre-scenting has worked like a charm for me. Mine had in his smaller enclosure wrestled a rat around a bit and then tried the middle and dropped it, similar story.
I just picked it back up and re-warmed it presented it a second time holding it (BBQ scissors-tongs) past the rear legs (rats legs that is) my guy struck constricted (second time) and had a better position to take the head.
I decided that in my case this was a small enclosure limiting his manoeuvring room. I put him in a larger one and this trouble went away. I don't know if this will help but that was what my problem seemed to be. Just don't stress him out check your temps and such and leave him be for a bit and try again next feeding day.