My 1976 edition of the Boeing 737-200 FCTM which was much more detailed with explanatory notes than the current dumbed down FTCM Boeing 737 series, displayed a diagram showing where the heels should be for take off and landing.
In both cases the heels were on the bottom of the rudder pedal and the toes were obviously higher up but just clear of the top of the brake pedal. In practice this was a most uncomfortable feet angle and most of the crews I worked with on the 737-200 in those days disregarded that FCTM advice. Mind you the -200 did not have the RTO facility.
Later editions of the FCTM had that diagram removed. In my experience there is a demonstrable danger of inadvertent rudder pedal pressure being applied if the heels are not on the floor as experienced in the first post. Accident records appear to show that there is more risk involved in a high speed rejected take off than with a continued take off. In any case, with the RTO facility up there with weather radar as one of the most significant advances in flight safety in recent years, there are now less risks involved in rejected take off's than in the old days.
Nevertheless it is usually better in the long run, to be go-minded. Yet I still see pilots in the simulator that during the take off run have their hand wrapped around the thrust levers like a claw poised to rip the thrust levers back right up to V1. This is a learned gimmick and looks rather quaint as well as useless, considering it only takes a fraction of a second to close the thrust levers using normal hand grip