On the order of rules specification

Question

I wanted to understand how Mathematica parses function definitions in rules-based programming, so I started with the simple code:

Clear[f];
f[x /; MatchQ[x, {_?NumericQ, _?NumericQ}]] := Total@x;
f[x_] := -1;
f[{1, 2.3}]
f[{4}]

As expected, the output is:

3.3
-1

Then I added another line:

Clear[f];
f[x /; MatchQ[x, {_?NumericQ, _?NumericQ}]] := Total@x;
f[x ;/ MatchQ[x, {_?NumericQ, 0}]] := (2 * x)[[1]];
f[x_] := -1;
f[{1, 2.3}]
f[{1, 0}]
f[{4}]

Interestingly, the output is now:

3.3
1
-1

So the second rule specification did not really override the first rule. But now, if I put that second rule before the first rule, like so:

Clear[f];
f[x ;/ MatchQ[x, {_?NumericQ, 0}]] := (2 * x)[[1]];
f[x /; MatchQ[x, {_?NumericQ, _?NumericQ}]] := Total@x;
f[x_] := -1;
f[{1, 2.3}]
f[{1, 0}]
f[{4}]

I get the expected output:

3.3
2
-1

So, I am guessing if I want multiple rules, I should put the more restrictive ones before the general ones. This way, Mathematica will be able to use the first match to execute the appropriate function. But now consider this:

Clear[f];
f[x_] := -1;
f[x /; MatchQ[x, {_?NumericQ, _?NumericQ}]] := Total@x;
f[x ;/ MatchQ[x, {_?NumericQ, 0}]] := (2 * x)[[1]];
f[{1, 2.3}]
f[{1, 0}]
f[{4}]

The most general rule is at the top, yet the output is:

3.3
2
-1

Can someone please explain why Mathematica didn't just see every input as matching f[x_] and simply return -1?

Thanks in advance.