https://opeforum.com/threads/clutch...-properly-deflect-chips-ms660-xl-s-etc.26571/
^thread I'd made before finding this one, I updated w/ pictures comparing WCS V Stihl-XL (462&500i covers, post 12) and thread's been updated w/ various other models's pictures (posts 8&9) it seems wider bottom, tight choke to prevent chips coming-over clutch, and long/vertical rear wall (typically rubber flap 'chute') to prevent excessive rearward spray... Didn't even consider hand protection til people mentioned it there, cannot say I'd want to add a single ounce to my 660 & don't need extra protection there especially at the cost of extra weight (thinking of the WCS units in-particular but even Stihl XL has a long flared bottom that extends the length of the cover when only the rear-most is necessary)
Found both of these breaking-in my 660 builds, lack of good & wide logs lead to burying the 32" & noodling 1' tall logs (fully buried bar though), in practice it eats through them so quickly this way (Live Oak at least) that it's no real use for 'in wood' testing/break-in's but is a good "initial cut" nice & soft & easy on the saw when breaking-in a brand new top end.
Dogs seem to need to be in pairs, at least for a smaller guy like me, singular dog on my 660 felt so wrong and the ebay XL pair on my 590 lets me push it so much harder (can usually push that 20" fully buried through anything at the speed I like, about on-par w/ 32" on the 660)
("holding back" is
both keeping away from chip buildup and just part of normal "see-sawing" through a piece, right? It's kinda how I've fallen into doing it, but I mostly go from videos am rarely around sawyers I can learn much from unfortunately)
Which cover are you referencing? On the XL Stihl OEM's (or the WCS's Stihl XL), you need to get that XL cover to use the big rubber deflector...supposedly (I have to wonder how hard it'd be mounting that inside a regular sized cover, I mean if the boot fits in-between the body & the clutch it almost
has to fit inside the stock casing by default...)