Postage stamps with depth < 20 do not report accurate utilization

[agazso]

Context

Bee 1.7 and lower versions

Summary

Postage stamps with depth < 20 do not report accurate utilization. The suggested workaround is to use minimum 20 for depth, but this may make low capacity postage stamps 8x more expensive than it is required (where depth is 17).

This also makes it confusing for people who just try out the postage stamps and choose the minimum possible value and then they don't understand why their postage stamp utilization is reportedly high.

If there is a theoretic difficulty behind this then maybe it would make sense to say that the minimum is 20 and enforce that in the API.