Most of them do drop a little so yes, it isn't anything strange. That's why I said after you get it to not drop then fatten it up until it does drop a little. I found my engines like to be just a tad on the fat side on the low end. I have one old YS that drops a big bunch when I remove the driver. I'm thinking it's just old age and telling me it would like to be freshened up a bit. Thing is the engine just runs so darn well I don't want to open it up for a rebuild. If the engine is in tune and running well don't over think it, just enjoy it. Don't try to squeeze every RPM or ounce of power out of the engine unless you are a racer. The old addage, the top end has no effect on the low end but the low end effects the high end is true up to a point. Stuff can happen though. I'm also lucky, where I live I haven't any big weather changes or problems with humidity so I almost never touch a needle after I have the engine set. As winter moves in on us I do have to fatten up the high end a little at a time. When it gets down into the 30s and 40s from a norm or 100+ my high end will be about 4 clicks fatter, the low end doesn't seem to be affected.