Hi @Dmitry ! Glad you're getting some turns in this season!
This is a subject that many folks who tour with packs encounter: you ski your setup unloaded and get the 'feel' of the ski/boot system- where it skis best with your weight distributed fore/aft, etc.- then put on a pack and all of a sudden you've got burning quads and the ski just doesn't feel as quick or responsive.
While forward lean is something to consider, it's not the only factor. On the surface, it looks like if a skier has added 20-30 lbs on their back behind the center of gravity, we can just change forward lean to rebalance weight about the center of gravity. While this can help some, it won't resolve the issue entirely.
The real crux here is the concept of 'sprung weight'. Your legs are the 'suspension' and everything above your hips is the 'suspended' or 'sprung' weight. For most folks, the weight distribution above the hip to below the hip is about 60:40. if we take a hypothetical 175lb person, that equals 105lb above the hips- not counting gear/clothing.
If we add a 25lb pack to that person, that's a ~23% increase in weight that the legs need to carry uphill and then work as a 'suspension' to support while skiing. More off-axis weight up top that the legs have to maneuver around in order to move in the direction you want to go adds even more effort. It gets easy to see why legs get tired so much quicker when carrying a pack.
That said, forward lean is an issue that can help correct for this to a very slight degree. I would resist the urge to change the fit of your boot to accommodate a pack, however. Changing things here can have unexpected and significant consequences to the way you’re able to ski.
I’ve found an appreciable difference in how my skis mounted with different touring bindings feel while skiing with a pack. Part of this is a result of the difference in binding ramp angle between bindings- that is, the delta of difference in heights between two binding’s heel and toe pieces. There are surprising differences between brands and models. Here’s a chart from Wildsnow that shows those measured differences. I feel a significant difference between skiing Radicals (∆15.16mm) vs. skiing Kingpins (∆9.7mm). This may seem insignificant, but using a little geometry, we can figure out that even this small ~5.5mm difference at the foot ends up shifting the center of mass of your torso/pack rearward about 100mm, causing your body to have to work differently in each binding to correct the imbalance.
These are all just interesting factoids, and no cause to go obsessing over whether you’ve got the correct binding. The simplest solution is just to pack the heavier items in your pack closer to your back, keep it cinched as snug to your body as is comfortable, and keep doing leg blasters on your off days to make those quads strong.
Hope this is helpful, or at least interesting- -Enjoy your turns!