This is one of my older posts but it should give you an idea on where your studs should be mounted. With the broader based studs that are used for rubber soles, use less of them than on the Weinbrenner boots.
I was a boot tester for Weinbrenner Boot Company, the manufacturer of the Gary Borger Ultimate Wading Boot. During in my years of testing I learned that not all studded boots are equal. It is better to have too few studs than too many.
Studs do not cause you to slip on rocks. What causes you to slip is the distribution and projection
of the studs. The distribution must be planned so that both studs and felt/rubber sole
contact the surface of the rock. Too many studs too close together and you are standing on the studs alone and not on both sole and studs.
The studs should project only a bare minimum from the sole. Early prototype versions of the Borger boots had the studs projecting too far from the felt sole and was corrected on the production model. Body weight will compress the felt and the studs then contact the rock and cuts through the algae. As the sole gets worn, more and more of the stud gets exposed. It the boots starts new with exposed studs, this does not allow for wear of the sole.
A stacked heel is doubly important if you are going to have studs so that you have this surface on the top of rocks. Too many studs and the corner of the heel may be the only non studded surface on the rocks.
If you have a higher quality boot like this Weinbrenner Borger Boot that has a "stacked" heel made of separate stacked, glued and sewn pieces of felt, the corner of the heel forms an edge that "grabs" onto the surface of a rounded rock and gives you a stable hold on the top of the rock. Imagine this boot on a rounded rock and you will see what I mean. Although the boot is studded, you cannot see them. This is how studs should be mounted.
The bottom of the Borger boot shows that the area under the ball of the boot has no stud but as you rock your foot forward, the studs begin to grab. Also notice that on the side view of the boot above, you cannot even see the studs because only the tips project from the boot. As you step on the felt, the felt compresses and the tips of the studs contact the rock and river bottom.
I tested two pairs of boots (studded and unstudded) made in Korea that Weinbrenner was thinking of marketing in the US under the Weinbrenner name. I fell off a rock and dinged my reel because they had a one piece sole with flat heels and a poor stud pattern. I recommended changes to the design but they decided not to market the boots.
The stud pattern is way to tight on the studded pair. The stud pattern must allow both felt and studs to contact the ground/rocks. That way, when you are on a rock, you are not on just the tips of the studs.
What did I do with the boots? Sold 'em on Ebay cheap. Unfortunately, even new current boots are still made like this.
Design matters! You can't just put a layer of felt or rubber on a one piece sole with a rounded elevated one piece heel and expect it to grab the top of a rounded rock. Note that the felt of the Borger boot is not only glued to the welt but sewn to the welt. A glued wet can pull off, a sewn welt will not.
Quality boots cost more but if they save a fall, they are worth it. I wish they could make them lighter but these boots last forever. I was a tester for the the prototypes of the Propex (ballistic nylon) boots above. I still have them and they are going on 20 years although they need new studs and soles. The boots are solid and have not blown out the sides or the toes.
Not all wading boots are equal and I think it is really important to have a separate stacked heel on felt sole, because there is no tread pattern on felt to provide grip when on slippery surfaces. As a boot tester, I got to keep the boots I tested, but some boots are not worth keeping even if they were free. I can't imagine buying boots that are unsafe just to save the cost of making a separate heel piece.