Unfortunately, you cant assume a reel will hold half the amount of line if the diameter is doubled. I attatched a picture of the spool equation, and the length of line you can put on a spool is inversley proportional to the SQUARE of the line diameter. This means it isnt going to be half the capacity for double the diameter. I also attatched a picture of the graph of y=1/x^2 which is the spool equation assuming the reel factor is 1 (it wont be in real life, but this is just to illustrate). You can see if you go from 1 to 2 on the x axis (doubling your diameter), the y axis (representing capacity) decreases by much more than half.
Where this gets more messy is with spools that dont look like the one in the picture, such as SV spools with the curved section on the inside. I believe the 19 morethan has a similar shaped spool.
I use this calculator to find how much of a given diameter i can fit on a reel. It wont be exact because some companies lie about line diameter, but so far with varivas line and both the steez a tw hlc, and antares dc md it has been spot on. Both of these spools are very similar to the basic spool shape in the picture tho, and varivas seems to have pretty accurate diameter ratings.
https://www.pattayafishing.net/fishing- ... estimator/
I plugged in your numbers, and it gave me an estimate of 61 meters of 0.381 diameter line for the morethan spool.
I know this was a lot of info, but hopefully it explained it well to you and will save you money in the future
