yep sure im 21 prospector and 18 surveyor...forgot it: my finder tk-220 + 3 depth enhacers (I, II and III)
oh one thing at first: you havent maxed the finder. Thats why you cannot expect maxed results with it.
id say your skills are nowhere near to be able to handle this setup. The depth enhancers alone should add 5 level each to the sib of your finder. Take the level of the amp you use and also add them to the sib of your finder.
So i wouldnt touch a TK-220 tier 3 depth enhanced with Level 7 amp before level 44 prespector/surveyor (22+15+7). You might think this is probably a bit overcautious. But those numbers are my formular for the safe side, where the weakness of my skills do not hamper my mining, i can drop a gazillion bombs and my results will just stay normal. When i amp too high or use too many depth enhancers (or both) i fell my return change drastically to the bad side.
So what should you do in my opinion? Put the TK-220 into your storage, at best use it unamped for "prospecting" meaning finding orespots. Depth Enhancers can be used on a smaller finder. Buy a finder thats maxed around level 12 and amp it with level 7 amp
OR use 2 depth enhancers on it (max!). Have you ever thought of using a F-105? Its a great finder around level 20, i also like Z15, Z20 and Z25 to skill up.
There is a third part of the story: the ressources. The prospector level and the sib ladder of the finders are responding to a sib ladder of ressources, provided you mine in an area where you can find those ressources. The tt value of a single unrefined unit of your ressource gives a hint, where to put it on the ressource sib-ladder. But its not that easy, we had 4 generations of finders and along with it, four generations of ressources on calypso alone. It takes some hundred thousand drops to get a full picture.
Last but not least a word about depth. People think the deeper the better. I disagree! I saw a lot of Narcanisum turn to Terrudite when i mined too deep. Today that might be good, but back then narc had 135% and more MU and Terrudite was tt-crap. Additionally i had maxed Narc but i was nowhere near maxing Terrudite, so it always came in small quantities, while i had a nice ammount of narc hofs. I still havent maxed Terrudite thats why i dont try to mine it.