Muffin Top
Here's my trick. Bottom line both glue surfaces must be faced, Willards tip tool always works, if you do it this way. Problem I see Nowadays, is layered tips have no Crown. This is where the problem lies, along with squishing glue with a tool made for this procedure.
Once both surfaces are faced equally, they must have the proper ''scratch coat''. Same thinking as a drywall or cement work. The grit of the sandpaper on the wheel is (PS22 in on the back of mine I just looked) is critical, it sets the depths of the glue. You don't want too fine or too coarse of a scratch coat. Like another said some tips/leather soak up more glue.
Ok, here's the trick....before you face up/glue the tip to the ferrule, attach with Very little glue, a tip with a crown to the top of your layered tip that has NO crown yet?
Next, on the layered tip apply an amount of glue that is a little too much. Touch tip/glue to ferrule facing, rotating tip/ferrule to make sure both surfaces are WET with glue.
CRITICAL....
Center tip as best you can by eye. Once it's centered....grab shaft, hold joint end at 12 o'clock and drop/bounce one time, lightly the tip off the counter, floor or any hard surface....
ONCE....re-center the tip and let dry. There is a nice EQUAL layer of glue between tip/ferrule, not compromised by a vice type tool. If the tip is flat, your NOT ABLE to do the drop squish/muffin top, it won't work. You must have a tip with a crown.
You'll notice....Now, the tip has a muffin top of glue sticking out all the way around, perfect. What you actually have done is ''hydraulically'' by Dropping the tip to a hard surface, you have burped out any possible air bubbles and evenly spread the glue amount to each face.
Muffin Glue....
no problem
What to do with the muffin top of glue? I use SG gel and in 20 minutes I'll take a piece of tin foil, wrap it around the shaft below the muffin top, then slid upward and turn the shaft removing all the muffin glue, thus not allowing it to get on the shaft or ferrule.
That's how I do it.