When you take cartridge base-to-ogive (CBTO) measurements using a calipers and a comparator insert, the tool seats on the ogive to where the bullet nose diameter matches the hole diameter of the comparator insert. This will not necessarily be the exact same spot on two different brands of bullets. Exactly where the insert seats (i.e. how far down the bullet ogive, or nose) depends on the ogive radius of the bullet. Different bullets will reach the diameter of the comparator insert hole at different distances above the bearing surface. This is because the ogive radius for two different brands of bullets can be very different. There can/will be variance in the ogive radius even within the same Lot# of bullets, although it's usually markedly less than between two different brands of bullets as shown in your picture. Because the diameter of the bullet nose at a given point above the bearing surface is dictated by the ogive radius, the observation you have made also means that the points at which two different bullets first contact the lands at "touching", and therefore how much bullet nose extends into the bore past the contact point cam also vary. So don't be concerned. The bottom line is that what you are experiencing is normal, even expected.
Likewise, COL measurements can and will vary with different brands of bullets, or even bullets from within the same Lot#. This is because the bullet nose lengths above the comparator insert contact point can/will also vary. Unless you have length-sorted bullets to a very small increment, it is therefore not totally uncommon for two loaded rounds to different COL measurements, even if they had the same CBTO measurement. Again, you'd generally expect this difference to be larger for two different brands of bullets, but not necessarily zero even for bullets from within the same Lot#.
Because of the [typically much larger] bullet length and ogive radius variance between two different brands of bullets, the key is produce as consistent as possible CBTO measurements for a single specific bullet type, as determined from measurements made using a tool such as like the Hornady OAL gauged or stripped bolt method for finding the distance to "touching" the lands. As indicated above, CBTO measurements made at "touching" for two different brands of bullets, or even two different length bullets from the same Lot# can and will vary. So it's important to find the distance to "touching" with every different brand of bullet you test. A measurement made with one brand may be very different than another, as illustrated very nicely in your picture above.
Even for a single Lot# of bullets, I set aside 10 bullets chosen at random (i.e. unsorted), label them #1 to #10 on the base with a Sharpie, then use the entire set of 10 bullets to measure the distance to "touching" with a Hornady OAL gauge, as well as COL. I then then take the average of the 10 measurement values to begin the reloading process (i.e. CBTO and COL at "touching"). I label the set of 10 bullets with the bullet info (i.e. Lot#, bullet type/weight, etc.) and keep them as my "measurement set" for that particular Lot# of bullets for as long as I am shooting them. That way, when I need to re-optimize seating depth, or make some comparative measurements to evaluate land erosion, I am using the exact same set of 10 bullets every time for the life of that Lot# of bullets. Some might consider taking 10 measurements every time excessive. It could certainly be done with fewer bullets than 10; for example 3, 5, 7, or whatever number someone felt comfortable doing.