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

t= int(input())
for i in range(t):
    n= int(input())
    a= list(map(int,input().split()))
    maxel=0
    maxindex=-2
    for i in range(n):
        if a[i]>maxel:
            if i>0 and i<n-1:
                if a[i]>a[i-1] or a[i]> a[i+1]:
                    maxel= a[i]
                    maxindex=i
            elif i<n-1:
                if a[i]> a[i+1]:
                    maxel=a[i]
                    maxindex=i
            else:
                if a[i]>a[i-1]:
                    maxel=a[i]
                    maxindex=i
    print(maxindex+1)                