I now do the same 6m/6m after previously living in Thailand continuously since 2011. I hence looked into the same question for myself. I reached the following conclusions.
No Fixed Rule: There's no absolute rule that staying in the UK for 6 months guarantees you have proven that you are maintaining a UK habitual residence. It's a guideline, not a legal threshold (unlike Statutory Residence Test, but this is a completely different consideration). Each case is assessed on its own merits, considering various factors beyond just the length of stays.
Keep UK Ties Strong: In order to demonstrate strong UK ties maintain a UK address, bank accounts, and show regular communication with UK institutions and if possible demonstrate existing family ties. This is only required if there was an investigation, but this is unlikely to happen when you are in the UK for 6 months.
Pattern of Stays: Regular patterns of long stays could influence any DWP's assessment, however any trips back to the UK, even short trips demonstrates ongoing ties to the UK. The longer the stay the stronger the tie to the UK.
Even on the very small chance you are investigated and lose the case there is a procedure to demonstrate how you can become a UK resident again by doing normal thing like showing where you are living and proving you are paying bills for the stuff that you consume in the UK (for things like utilities and groceries over a two or three months period). Hence theoretically there could be a small period when indexing was lost however its quickly retrieved and you should have no problem in doing this.