Yes. Think of the problem in terms of the production/flow rate. The rate is too low; the size of the SHBG reservoir doesn't much matter.
The range of 16-31 ng/dL for Tru-T is not a general population reference. It is a target therapeutic range as explained in this post.
"Based on the new data on the distribution of free testosterone levels in healthy men the target range of free testosterone has been determined to be 164 to 314 pg/ml (mean+/−1SD)"
I vote for a combination. Maybe you had above-average SHBG that increased some over time. Meanwhile your free testosterone set point declined a little. Both results are considered to be a normal function of aging.
