Mas Ganjawulung, I believe you've already gave some good explanation regarding keris tindih.
IMHO, tindih, in this context, would be better to be translated as 'suppress'. So, keris tindih is a 'suppressor' to, as Ganjawulung already said, the negative effect of 'bad keris', usually a keris which has 'panas' ('hot') or 'galak' (fierce) attribute. Why do we keep such a bad keris ? Perhaps because it is a fine and rare blade, or more commonly, because we simply don't know which one is bad, and as precaution, we keep a 'suppressor', just in case. At least, it gives a relief to it's believer.
Why jalak/bethok budho? Budha or budho doesn't mean Budha (religion) in this context. In Javanese context, it means archaic or ancient. In Javanese language, 'wong budho' means a simple and naive person. Thus, jalak/bethok budho is archaic/ancient jalak/bethok. It should be made from 'besi budho', the oldest iron. It is believed that the 'tuah' of besi budho is 'asrep/dingin' (cold), and the empu's prayer while making this blade is to bring 'slamet' (safe/wellbeing) to the bearer. 'Slamet' is a very strong word in Javanese culture. IMHO, it could take an exclusive book just to explain the meaning of slamet and it's important position in Javanese culture. Thus, armed with besi budho and empu's prayer, jalak/bethok budho will suppress (or 'lerem') every hot and fierce kerises. In the 'spirit point of view', no younger spirit who resides in younger, hot and fierce kerises would dare against an old,wise and 'ampuh/sakti' priest who resides in jalak/bethok budho. Then, they should behave accordingly.
Keris Sombro, and any other 'bethok' is also believed to have similar characteristic to jalak/bethok budho, especially in empu's prayer. Ni Mbok Sombro was a woman, so in the 'spirit point of view' : Since there is a lady in the house, all the naughty boys should behave and being polite
Gold is also believed as having a neutralizing effect. Only 24k gold works, and this time, 'neutralizing' is a proper word. Some elders prefer keris without gold as powerful pusaka, since the presence of gold would nullify or at least reduce it's potential power. So, use gold sparingly
Please remind that some kind of serasah/inlay and rajah, e.g. kala cakra and raja sulaeman, are believed to add 'more power' to the keris.
It is worth to note that what I've described here is common beliefs in Javanese or Javanese-influenced collectors. Any other beliefs/opinions may exist, and sometimes against each other. No 'right or wrong' answer here. All true to it's believers. Other keris culture may also vary.