inductor - Extent of ground plane beneath filtered DC converter?

I'm laying out the PCB for a small and simple power supply to feed some audio amplifiers. It will feature a DC -DC converter module and I'd like to filter the output for 1) extra smoothness 2) learn about power supply filtering. So I found this courtesy of TI:-

I'm using a TRACO converter rather than TI, but otherwise the circuit is the same. The switching frequencies are similar. They're both 2W - 3W power. So a 100uH ferrite inductor looks like:-

If I were to have a ground plane on the backside of the PCB, do I back it off from the inductors (and converter)? Consider that there will be inductors inside the converter. That's three inductors. Do I put three holes through my ground plane, or keep it solid?

I looked at one question that suggests keeping the ground plane solid, whilst the answer for this one suggests a hole. I'm confused again.

Further confusion arises from some cheepo converters I have from on-line. You'll have probably seen one of these fairly ubiquitous thingies:-

These have a solid ground plane on the reverse side. Is that just 'cos it's easy /simpler or are cutouts unwarranted? Clarification would be most appreciated.

Answer

That round Siemens inductor will have lots of external field lines, because there is no closed path. The air path is 1cm or 2cm (10mm or 20mm)

The cheapo switcher inductor looks like a black tub with central core, and the flux only has 1mm or 2mm air path, thus much less external flux to be a bother.

That round Siemens inductor will induce voltages (Faraday Law induction) all around on the PCB.

Find a closed-ferrite-path inductor to use.