You are getting the correct amount of mana per cannibalize. This has been a client side bug for a long time. On the server, the numbers are correct, which is the important part. The numbers you see on the client are not always accurate when cannibalizing, and you need to wait another few seconds for the numbers to correct themselves.
When you are canni dancing, just wait until the number has changed. It doesn't matter if the number is correct. Once you see the change, you are in between ticks now.
The numbers do sometimes change in between ticks while cannibalizing, which can make it difficult to determine when the tick is. This is why I usually canni dance every other tick. When you initially see the number change, do the dance. You will then probably see the number change again relatively quickly. That is the numbers being corrected. If you canni dance every other tick, you should see the numbers calm down first, before the next change occurs.
I made this macro a little while ago to help with canni dancing every other tick. This macro will allow you to canni twice within 6 seconds. This means you are still getting the numbers for a canni dance every tick, but you can do the easier strategy of dancing every other tick. This macro will not work for Canni 4, due to it's longer casting time.
/stand
/pause 1
/pause 21, /cast 1
/pause 21, /cast 1
/sit
This macros DOES require a global cooldown refresh item, such as
https://wiki.project1999.com/Spyglass . This macro DOES require canni to be in the top most spell slot. The top most spell slot acts a bit differently than the other 7 spell slots. You can use a global cooldown refresh item to make the spell clickable again, even while it's recast time cooldown is occuring.
When you see your mana numbers change, hit this macro. You will stand and cast canni for the first time. As soon as the first canni is finished, activate the spyglass.
The easiest way to do this is to bind your macro to a key such as the number 1, and bind the clickie to the next number, such as number 2. Press 1, wait for the first canni to finish, then press 2.
That will refresh the global cooldown, and the macro will cast canni a second time. Then you will sit down. This will all happen in under 6 seconds. Then you can basically wait until the numbers calm down, and canni every other tick.