If you tend to stay behind the ball when you throw spare shots, your track will be higher. I can hear my spare ball rolling over the thumbhole as it goes down the lane.

With your strike ball, you are probably coming around the ball more, which could result in a lower track.

Pin positions and balance holes CAN and WILL make a difference in where your track is. The lower the pin in relation to your grip (such as a RICO drill which places the pin in the palm). If someone tracks high, this person may have issues tracking over the fingers and/or thumb with that drill as I do. Because I stay behind the ball so long, I usually have to place pins ABOVE my fingers to help lower the track. Basically, the higher the pin in relation to your grip, the lower the track. When looking at drill sheets, some have a "drill safe" zone for higher track players.

When I had drilled some stuff with lower pins and ended up thumping the ball over my fingers and thumb, I would add a thumb quadrant balance hole if a balance hole was not in the ball already. By positioning the balance hole in a specific location in relation to the pin through your grip, you can lower your track without altering the pin location on the ball or your release.

I release the same way for strike and spares.... I tend to thump down the lane with spares, and depending which strike ball I'm using, I tend to edge the thumb or be an inch from the thumb. One ball l'll flare over the thumb always.

The first flare ring by my fingers are very similar with both strike balls and my spare.
also, Sometimes what a person feels at release isn't what they are actually doing. Videos don't lie.

I have to add, both my strike balls have the same layout. The one that flares over the thumb always has a layout 45x5.5x75 which puts the pin below my middle finger.

It's the difference in ball construction that causes you to track higher with the plastic ball.

EVERY bowling ball had a core it more relates to core strength...the stronger the core the more potential the ball can flare or rotate before actually contacting the lane...another fact is most cannot see the initial flare rings on a bowling ball...unless you track the actual pap off a players hand you cannot assume a pap

If you can place a quarter over desired spot...pin to pap or pap is close enough