The issue is that this head, together with FM's no-longer-produced custom socket, is engineered to focus with ONLY two lamps; one is the readily available Carly CL1499; the other is the FM1794 (custom-made by Carly for FM), available from only one source (not FM). Other bi-pin bulbs like Streamlight (Strion, TL-3, etc.), when used with FM's socket, are too short; they won't focus. Stock Surefire LAs, as well as LumensFactory LAs, are also too short.
The socket in the E2-Fire body sits even further back. With this head on that body, none of the above lamps/LAs will focus; including the 1499 and 1794.
It would be nice if FM made a turbo-head that would focus with "stock length" lamp assemblies. It could be used on stock/custom E series bodies with all the stock/aftermarket E series incandescent LAs, as well as custom E series LED tower modules (like Veleno Designs'). It could also then be used on the E2-Fire with the 1499 and 1794; in other words, design a turbo-head that could be used anywhere a stock E series bezel can.