A small coil would be for trashy areas and for getting close along fence lines and metal poles. You have to work them slow. As far as depth I would say you would get 6 inches on a 5 in. coil max. They hold a great place in your arsenal of coils. All I use are 3 coils a 5 in. and 8 in. concentric and my 13 for large fields. This covers all my needs.
From everything I've read,and I've been doing a lot of looking for info on these coils. The stock brand 5" t 2 coil is a good coil. People really love the Nel sharp shooter coil or the Mars sniper coil. Detech makes a 8 x 6 Sef coil, you can find them from England but the price and shipping isn't real horrible.
Thanks for the feed back! Do any of these alternative coils have the same connection port for a T2? That would be my only question regarding an alternative non-Texas First coil.
NEL Sharpshooter or CORS Fortune (rebranded NEL..for less $$)
I didn't like the stock T2 puck 5"
IF You go with NEL/CORS make sure it is the one for T2, it specifies "for T2 only" unlike others that may work on several machines.
I'm not exactly sure of what you are asking but they are machine specific. You must buy a the coil that is stated for the T2.I'll post some coil examples from our sponsors here. It may not be the coil type you re asking for.
https://www.kellycodetectors.com/catalog/15x12-sef-butterfly-search-coil-teknetics-t2
https://www.kellycodetectors.com/catalog/10x12-sef-butterfly-search-coil-teknetics-t2
https://www.kellycodetectors.com/catalog/13-ultimate-dd-search-coil-teknetics-t2
http://www.colonialmetaldetectors.com/nel-sharp-coil-teknetics-t2.html
http://www.colonialmetaldetectors.com/nel-sharpshooter-coil-teknetics-t2.html
http://www.colonialmetaldetectors.com/nel-hunter-coil-teknetics-t2.html
I hope this helps.