Of the 6 fonts in Adobe Caslon Pro only the regular and semi-bold have true small caps. Neither the bold nor any of the italics have true small caps. You can verify this by clicking on the individual fonts here. Also I checked by opening the fonts in Font Lab.

So I think what is happening is that you are getting fake small caps for the Bold, as you would for any of the italics, small caps that are constructed by InDesign by formula from the caps. And what you are controlling for is the size of fake small caps. InDesign defaults to the real small caps when they are present in the font. Real small caps are not adjustable—but they will look better than fake small caps.

When you click on 'small caps' in Indesign you are only *supposed* to change lower case into small caps. To get all small caps open the character dialogue box, hit the top right corner, then choose "open type", then choose "all small caps". That will turn both caps and lower case into small caps. Then you will get real all small caps in Adobe Caslon Regular and Semi-Bold, but not the four other styles.

If you want true small caps for a Caslon italic, check out this version of Caslon. I think both the roman and italic are better in text than Adobe Caslon, but I'm a biased source.

William's design comes highly recommended.

If you're stuck with Adobe Caslon, you might consider
commissioning the customization to fill in the missing
pieces. Adobe is rare among font houses in being highly
liberal concerning modifications, and there are a number
of people here who could do it for you. Including yours
truly! hpapazian at gmail dot com

hhp

William – Went back and had a good look at ACaslon Pro. I now understand that the natural form of the 'small caps' for Reg and SB has a proportionally large initial cap ... was expecting it to be less so. Open type 'all small caps' was being used in my document hierarchy, but was just looking to add something a little more 'busy'. Will continue working within the font set and see how it goes.
Checked out Williams Caslon – an elegant cut. YES, VERY BIASED!

Hrant – thanks. I rarely link to typophile ... only when desperate. I always smile, seeing your inciteful words in whatever forum I end up in.

The “Small Caps” command only effects lower case letters.

There are a few fonts* with two or more sets of small caps ( usually Regular and Petite), which would give you the degree of busyness you’re after, i.e. no commonality with the default Upper and Lower Case setting.

*e.g. the profuse FF Atma.