Phex will not extend the query range once 200-300 results are returned. This is done to reduce the network load and to complies with the rules to be a "good Gnutella citizen". Searching for words like 'mp3' are exactly the reason why this is done. The query will likely travel only one hop and cause enough results to be returned in short time. Phex figures that the query is too popular and dynamically reduces the search horizon or maybe even stops the whole query. On the other hand if you search for rare content with few results Phex will extend the range to reach more hosts.
In case slow host still return delayed results they wont get rejected though and displayed.

I recommend you to further refine your query with more specific search terms.

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