Kontact give you some decent metrics to start with. Here's some of the rationale behind it.

Sitting far forward is good for generating power on the downstroke, but it's exhausting for the upper body and putting all your effort into the downstroke is not healthy for your knees, muscles, and blood vessels. Sitting essentially behind the crank axis (bottom bracket) is more efficient for upper body balance and pedaling "round." Pedaling round means applying pressure to the pedals according to their circular movement with your feet and ankles, as opposed to "driving piles" or "pushing pistons." Your legs are not connecting rods.

Sitting too high discourages pedaling round. If you have to rock your hips or point your toes to reach the pedals at the bottom of the stroke, you're too high. If you're bouncing in the saddle as you pedal faster, you're too high.

Learn to pedal faster to go faster, rather than depending on larger gears. It's healthier for your cardiovascular system and legs and it will eventually enable you to ride faster and farther. There are numerous articles and videos on positioning, cadence, and pedaling technique. Most of them are to some degree helpful.

I'm telling you this so you can avoid the mistakes I made as a beginner over 50 years ago.