Yes, as commander Ian Doncaster mentioned, I'm currently working on another (hope the last one) attempt to organize all our present knowledge about Tip Off game mechanics, and in fact that was started as general surface crash sites classification/mapping/prospecting, Tip Off missions being a good source of the latter.
As far as I understand commodities and mats one can obtain at a given site are functions (quite strict) of the site layout (model) with some randomizing multipliers applied. There are only some dozens of those layouts/models available in game (i.e. number is limited as they are hand-crafted) and hundreds (or much more) permanent and semi-permanent locations (also we can take into account random POI encounters).
I'm collecting this data (and for the most part of known TO sites in the Bubble that is already done), however haven't finished to organize it (with some rare exceptions), so not all information is in the spreadsheets - big quantity is still in form of logs/screenshots and recorded video (~150 GB of data!!! - so the process is not something to accomplish fast).
With commodities this works supposedly like this:
1) let us say we've encountered layout "A" (for permanent and semi-permanent sites the layouts are "nailed" and do not change without special external intervention).
2) note: visual appearance of the same site layout on different locations can have a slight difference depending of terrain as it looks like that for crash sites (contrary to planetary settlements or ports) the preliminary terrain "flattening" procedure is not applied (they are just dropped down on the existing one).
3) any layout always have a fixed number of commodities (or may be even better to refer to them as a commodity spawning points). That number is nailed to layout and doesn't change.
4) Each "spawning point" (or a group of them) have a predetermined (fixed) subset of commodities it can produce. Those subsets can vary from quite wide (like low-value food and drugs), or a single item (like Thargoid Sensor). As far as I understand Black Boxes, Occupied/Damaged Escape pods are usually members of the same subset. Honestly don't know if there are anything like "grades" defined in those subsets.
5)Finally time for RNGesus - choose 1 commodity for each point and gave them to commander. That is clearly instance-dependent and the final set changes on each relog.
Returning to Personal Effects. Haven't encountered them recently on TO-related crash sites in the Bubble. All locations with 1 eagle DBX (in fact it is the same one layout) have 1 "rescue" spawning point with BB/OEP or DEP. May be there is a chance around single condas (not "graveyards") or "unidentified wrecks" (UW)
EDITED: My bad - not crash sites with "Eagles", but with DBX's have rescue-related commodities.