Byzantine Follis of Justin II with Chi-Rho above M - "Special" Heavy Issue?

A couple years ago when I first started in on Byzantine coins, I read our local library's copy of Byzantine Coins by P.D. Whitting. There I found a reference to a chi-rho variation of the very common Justin II-Sophia follis from Constantinople (Sear 360).
Here is the quote:

"The copper follis comes down sharply in weight and size during the reign...with an average weight of 13.5 g. There was, however, at Constantinople from the 5th regnal year onwards, a heavier issue (by a gramme) in parallel, distinguished by a Chi-Rho above the M on the reverse, as against the usual cross."
(Byzantine Coins (1973), by P. D. Whitting, pp. 111-112)

In my own small collection, I now have four examples of Sear 360, two with the chi-rho, two the cross. Indeed there is a weight difference, pretty much in accordance with Whitting, but Byzantine coins seem to vary so much in weights I was wondering if a "gramme" difference can really be attributed to a specific symbol within this issue?

I have not had any luck finding other references to this weight change online. Examples of SB 360 abound, of course, and glancing through Coin Archives I saw some examples that conform to Whitting's information.

Valentinian's recent post on Anonymous follis variations shows there is an impressive number of Coin Talk Byzantine experts out there - does anybody have any other information on this? Examples?

Here are mine. Such a small sample is hardly conclusive, not helped by the fact my "chi-rho" examples are quite worn, but again, the heavier weigh for the chi-rho does hold true:

The top two rows have the standard cross (year 11 and year 5): 12.15 and 13.93 grams

The bottom two rows have the chi-rho (both year 6): 14.61 and 14.29 grams.