There is a generic base sprue that comes will all Epic releases to date. This has 3 sizes of base. 60mm x 20mm for all infantry and cavalry, giving a linear look. 30mm wide for artillery. 20x20 for commanders.
Those base sizes are used throughout, so a 60mm base holds a strip of 10 figures, the same base can take 5 cavalry and the same base can take 4 - 6 individual skirmisher figures, so an Epic army will see 60mm bases throughout, whether you have a lancer, cuirassier, light cavalry, line infantry or skirmishers etc.
The Hail Caesar uses this generic base and also introduces a new base size, 50x50 and this is on the elephant sprue, so is specific to them.
Prior to hail Caesar, the infantry strips were 55mm wide, so fitting them to a 60mm base results in a small gap between figure blocks, which to my eye, disrupts the the look of a line when 2 or more bases are lined up.
My solution is to mount onto 55mm MDF bases instead.
However, I note that in Hail caesar, the lines of infantry have shields that extend slightly beyond that 55mm strip and so especially the round shields, reduces the impact of a 55mm strip on a 60mm base.
I am just setting my stuff up, but I have been really taken by the basing system that a YouTuber is doing, in which he has moved to 90mm basing. Here is a link, just to open this conversation to the possibilities that exist beyond the ‘official basing’
Link
https://youtu.be/JTA9yWCD5R0?si=LB2T8RaLVvAvCfeG