1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

import sys
#import bisect
#import math
import itertools
def get_line(): return list(map(int,sys.stdin.readline().strip().split()))
def in1(): return int(input())

for _ in range(in1()):
    n=in1()
    a=get_line()
    t1=max(a)
    t2=min(a)
    if t1==t2:
        print(-1)
    else:
        for i in range(n):
            if a[i]==t1 and i>0 and a[i]>a[i-1]:
                t3=i
                break
            if a[i]==t1 and i<(n-1) and a[i]>a[i+1]:
                t3=i
                break
        print(t3+1)

