Hot Tap welding procedures or "In-Service" welding procedures can vary quite a bit. It depends on a series of issues. One is the carbon equivalent of the carrier pipe and or sleeve. More conservative procedures would call out for buttering layers to be deposited on the main first, possibly ground down to a certain height (1/16" common) then the fitting positioned over this area. If your first buttering layer also contacts the fitting then additional filler passes may not temper the HAZ on the I.D. portion of that first pass leaving high hardness areas potentially. The welding procedure will specify the established pass sequence. The procedure should have been developed addressing issues such as carbon equivalent, flowing contents, service pressure and flow rate...among other things. The more severe the operating conditions or pipe chemistry the more conservative the welding procedure will be. So to answer your question directly, it all depends on pipe materials and operating conditions. I would have to default to the company established welding procedures.